In aviation or industrial fluid pressure sensors, isolation of electrical leads from corrosion and isolation of the pressure sensing film from mounting stress are both desired for long term reliability and accuracy.
Fluids (pressurized media) can corrode metal sensing films and leads. Metal sensing films are thus preferably placed inside a pressure sensor body and leads are also preferably routed inside the body and isolated in such a way that corrosive process fluids do not come in contact with the sensing films, electrical leads and electrical contact pads. Corrosive process fluids can include gasses in an aerospace or stationary turbine engine, acids, caustics, oils, petrochemicals, foodstuff and the like.
Mechanical isolation of the sensor from mounting and lead stress variations is also a problem, and there is a desire to arrange sensor geometry to reduce transmission of stresses from mounting and electrical leads to the pressure sensor diaphragm. These stresses often vary with temperature.
When layers of sensor bodies are bonded together using bonding materials, or when ceramic layers are sintered together at high temperatures, residual stresses can be left in the sensor bodies that are temperature sensitive and generate stress in sensing diaphragms, causing further errors.
It is difficult to find a combination of materials, type of bonding, electrical lead connections, mounting and sensor geometry that meets the demanding requirements for industrial and aerospace pressure sensor applications. Excellent isolation from corrosion, high monotonicity or linearity, stability, accuracy and isolation from errors due to environmental factors such as temperature changes and mounting stress changes are all desired, but difficult to achieve in a single sensor that will meet the needs of a broad range of demanding industrial and aerospace applications.
A pressure sensor capsule with improved isolation for a broad range of demanding industrial or aerospace applications is disclosed.
The pressure sensor capsule includes a pressure sensing body formed as a beam made of direct bonded layers of single crystal sapphire. The beam forms a beam wall around a central channel. The beam has a first end having a diaphragm adapted for fluid pressurization, and an opposite second end. The beam wall has an outer beam mounting surface between the ends. The central channel has a first width near the first end and has a second width, near the mounting surface, that is narrower than the first width.
The pressure sensor capsule includes an isolation plate. The isolation plate has a mounting hole therethrough and the beam mounts through the mounting hole. A braze joint sealingly joining the outer beam mounting surface to the mounting hole, sealingly isolating the second end from pressurized fluid.
Conductive film is disposed in the central channel. The conductive film includes a pressure sensing portion on the diaphragm, and a sensor lead portion extending from the pressure sensing portion to electrical contact pads. The beam has a notch at the second end. The notch forms an isolated lead surface on the central channel where the electrical contact pads are accessible.